We get many phone calls and emails, as well as see many forum posts, related to the trouble that can result when trying to service a totally dead battery. By totally dead, we mean “stone cold dead,” 0-1 VDC. In fact, despite the fact that it is unusual to find a battery in this condition, it is a relatively common topic on the forums, whether the specific situation involved is related to charging, starting or other applications. So, we thought we’d address this topic in this month’s article.
For many products on the market, a totally dead battery can cause serious problems. With many battery charging products (chargers and maintainers) sold today, a totally dead battery means you can’t service it, or, in order to service it, you have to play some tricks on the battery, such as connecting a second (charged) battery to activate the charger. This is because modern “smart” chargers need to sense the battery’s polarity before they will send power to the clamps. But, a totally dead battery has no polarity, resulting in what we call “The Dead Battery Dilemma”, i.e. “I bought a charger because my battery is suspect, but my charger won’t turn on because my battery is dead.”
This is not an issue with our PRO-LOGIX line of professional battery chargers and maintainers. If you are required to charge a totally dead battery, but your PRO-LOGIX charger won’t activate due to exceedingly low voltage (<1V), you can verify that all of your connections are correct and hold the CHARGE/START button down for three seconds. It will enter a Forced Start manual charge mode and then, when the battery rises above the sensing threshold, all safety features will kick in and the automatic charging process will take over.
Plus, our PRO-LOGIX chargers feature a soft start mode, such that, if the charger is connected to a severely discharged battery, it will first charge the battery at a low rate until the level of charge has risen to the point where it is appropriate to provide standard charging power. This protects the battery when it is most vulnerable and supports battery longevity.
To a lesser degree, a totally dead battery can also create problems when using a jump starter. These problems fall into two areas. The first is similar to the charging issue above – many newer jump starter designs require the battery to be above a certain voltage to sense polarity. The second has to do with how a totally dead battery impacts the jump starting event.
As with modern chargers, many of today’s jump starters, particularly lithium jump starters, have a safety feature where they need to sense polarity prior to allowing the unit to provide jump starting power to the clamps. This is a great safety feature and makes tons of sense. The problem comes when trying to jump a totally dead battery, which will not allow the jump starter to sense polarity and will, therefore, not activate. This is not an issue with Jump-N-Carry lithium starters. Our models JNC325 and JNC345 feature an override similar to the forced start charger function detailed above. In this case, if you are connected to a totally dead battery and confirm that all connections are correct, you can hold down the override switch for 5 seconds and the jump starter will engage, allowing you to jump start the vehicle. In addition, our traditional Jump-N-Carry and Booster PAC lead acid jump starters have no minimum voltage requirement and can even jump start a vehicle without a battery.
The second way a totally dead battery impacts the starting event is that the dead battery acts like an anchor on the starting process. When you connect a fully charged jump starter to a totally dead battery, the dead battery will immediately begin to drain the jump starter’s battery. This can create a significant hurdle to overcome in achieving a successful jump start. In fact, jump starting a vehicle with a totally dead battery is far more challenging than jump starting a vehicle with no battery at all. Because Jump-N-Carry and Booster PAC jump starters are so powerful and are designed to deliver long cranking performance, they are able to quickly and easily overcome the extra power demand involved in starting a vehicle with a totally dead battery.
This one is a little trickier, but still deserves to be addressed. There is no way to test a battery at or near zero voltage (stone cold dead). The battery is going to need to be charged (see above on how easy that is with PRO-LOGIX). The question is how much does the battery need to be charged to enable it to be accurately tested?
Like most questions in life, the answer to this one is, “It depends.” Primarily, it depends on the equipment used to do the testing. If using an invasive load tester, such as a carbon pile tester, you need to charge the dead battery to at least 85% State if Charge (SoC), roughly 12.5V. This ensures that the battery has enough capacity to withstand the test and provide an accurate result. Similarly, if using an electronic tester, there is still a level you need to reach, but it is considerably lower. For most digital testers, the battery should be above 8.0V to obtain a reliable, accurate reading. A battery with lower voltage is likely to be too unstable to provide a reliable reading, resulting in the tester bringing back a “Charge and Retest” result. Again, it varies by tester model (and even by the battery construction tested), but 8.0V is a good threshold for most.
After you have jump started the vehicle (in which case the alternator will recharge it) or have properly charged the once totally dead battery using a quality battery charger (such as PRO-LOGIX), your work isn’t complete. Allowing system voltage to drop below critical levels can have a negative impact on control modules and other system components. System operation should be thoroughly checked to confirm that there were no long-term negative consequences and that all system relearns have completed successfully.
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As noted above, we get a lot of calls, see many forum posts and speak to many resellers and technicians at shows about this topic. A totally dead (0.0V) battery doesn’t have to ruin your day or your service routine. In our product development process, we always consider how a new product will interact with and overcome a battery at or very near to 0.0V State of Charge. That’s why our products are able to effectively manage batteries in all conditions, even stone cold dead ones.
Have you ever had a run in with a totally dead battery that made your life difficult? We’d love to hear about it in the comments.
You should mention that it is bad practice to jump a totally dead battery and let the customer drive away. You should always instruct them to drive to the nearest garage and have the battery charged or replaced. To not do so is hard on the alternator. Back around 1980 – 2000 it was a particular problem with Ford. I have seen cars come in with alternators so hot you could have made toast on them! I imagine it doesn’t do modern electronics any good either. I know you often can’t diagnose computer problems without a fully charged battery.
Forrest – You make a really good point. Yes, allowing the battery to drain extremely low will cause negative impacts to various system components. As you state, this is particularly taxing on the alternator. These are great things for vehicle owners to keep in mind. Thanks, Jim from Clore Automotive
Like many Technicians in the trade, I have had my fair share of moments when testing batteries in a regular service job.
I have bought many testers over the years, hand held for 15 secs to test drop voltage, digital testers with no print feature and now Clore tester with printer.
My point is this, how do you know when to really trust a tester? Unless you have more than one tester in your toolbox.
I have been let down badly with a top brand tester( not mentioning name here) that I decidedto buy my current tester with built in printer AND, I do two tests to be certain.
Anthony – Thanks for your comment. You makke a great point. There are many in the trade who believe, like you, that a combination of digital testing plus carbon pile load testing is the best way to ensure that a battery assessment is accurate. I do not fault you for taking that position, as there is always going to be that outlier battery that fools one method or the other. So, doing both is the safest path to a reading you can be confident in. That said, I believe that, for the vast majority of batteries out there, a quality digital tester like our BA327 will provide a very accurate assessment. Again, thanks for adding to the dicussion. Jim from Clore Automotive